High throughput method of in transit wafer position correction in system using multiple robots

ABSTRACT

Methods correcting wafer position error are provided. The methods involve measuring wafer position error on a robot, e.g. a dual side-by-side end effector robot, during transfer to an intermediate station. This measurement data is then used by a second robot to perform wafer pick moves from the intermediate station with corrections to center the wafer. Wafer position correction may be performed at only one location during the transfer process. Also provided are systems and apparatuses for transferring wafers using an intermediate station.

BACKGROUND

Different types of tools are used to perform hundreds of processingoperations during semiconductor device fabrication. Most of theseoperations are performed in vacuum chambers at very low pressure. Wafersare introduced to the process chambers with wafer handling systems thatare mechanically coupled to the process chambers. The wafer handlingsystems transfer wafers from the factory floor to the process chamber.These systems include loadlocks to bring the wafers from atmosphericconditions to very low pressure conditions and back, and robots totransfer the wafers to various positions.

In performing the various wafer handling tasks, the wafer transferrobots use programmed coordinate information of the loadlocks, processmodules, etc. At certain points, the position of a wafer may need to beadjusted to correct for wafer shifting during robot hand-off, robotmovement or in a loadlock, process module or cassette.

Throughput—the number of wafers that is processed in a period of time—isaffected by the process time, the number of wafers that are processed ata time, as well as timing of the steps to transfer the wafers. What areneeded are improved methods and apparatuses for increasing throughput.

SUMMARY

Methods, systems and apparatuses for correcting wafer position error areprovided. The methods involve measuring wafer position error on a robot,e.g. a dual side-by-side end effector robot, during transfer to anintermediate station. This measurement data is then used by a secondrobot to perform wafer pick moves from the intermediate station withcorrections to center the wafer. Wafer position correction may beperformed at only one location during the transfer process.

One aspect of the invention relates to a method of transferring wafersfrom a first location to a second location. The method involvesmeasuring wafer position information of one or more wafers handled by afirst robot during transfer from the first location to an intermediatelocation and picking the one or more wafers from the intermediatelocation with a second robot for transfer to the second location,wherein picking the one or more wafers comprises using the measuredposition information to determine the trajectory of one or more endeffectors of the second robot during the pick move.

Another aspect of the invention relates to a method of transferringwafers from a first location to a second location. The method involvesextending a dual end effector arm of a first robot to a first locationhaving first and second side-by-side wafers to pick the wafers such thateach wafer is supported by an end effector; retracting the dual endeffector arm along a nominal path and moving the dual end effector armalong a nominal path to an intermediate station; extending the dual endeffector arm along a nominal path to simultaneously place the wafers atthe intermediate location; wherein position information of the wafersrelative to the end effectors is measured at some point during thenominal retraction, transfer or extension moves; sending the positioninformation to a second robot and receiving the position informationwith the second robot; picking the first wafer from the intermediatelocation with a first end effector of the second robot to from theintermediate location, wherein the position of the end effector duringthe pick move is adjusted based on the received position information;picking the second wafer from the intermediate location with a first endeffector of the second robot to from the intermediate location, whereinthe position of the end effector during the pick move is adjusted basedon the received position information; transferring the wafers to thesecond location along a nominal path; and simultaneously placing thewafers at the second location.

Another aspect of the invention relates method of transferring wafersfrom a first location to a second location, including the operations ofextending an arm of a first robot to a first location having one or morewafers to pick the one or more wafers such that each wafer is supportedby an end effector; retracting the arm along a nominal path and movingthe arm along a nominal path to an intermediate station; extending thearm along a nominal path to place the one or more wafers at theintermediate location; wherein position information of the one or morewafers relative to its respective end effector is measured at some pointduring the nominal retraction, transfer or extension moves;

storing and/or sending the position information to a second robot;picking the one or more wafers from the intermediate location with asecond robot wherein picking the one or more wafers comprises adjustingan end effector based on the position information of the wafer beingpicked such that each wafer is centered on the end effector;transferring the one or more wafers to the second location along anominal path; and placing the one or more wafers at the second location.

Other aspects of the invention relate to systems and apparatuses forperforming the methods describe herein.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an exterior of a dual wafer handling apparatusand components thereof according to various embodiments.

FIGS. 2 a and 2 b are schematics of a dual wafer handling apparatus thatshow an internal views of the atmospheric environment and the transfermodule according to various embodiments.

FIGS. 3 a-e are graphical representations showing top views of a dualwafer transport apparatus performing certain operations in dual wafertransport of a pair of wafers from a storage cassette to a wafertransfer module and back according to certain embodiments.

FIG. 3 f shows an example of a sequence of movements a pair of wafersmay undergo in a process module according to certain embodiments of themethods and apparatuses described herein.

FIG. 3 g shows a schematic of two arm dual end effector transfer modulerobot with one dual end effector arm in an extended position and theother dual end effector arm in a retracted position.

FIGS. 4 a and 4 b are schematics of a stacked loadlock according tocertain embodiments.

FIG. 5 a is a process flow sheet illustrating operations in a method oftransferring wafers using a dual side-by-side wafer transfer robot.

FIG. 5 b shows graphical representations of top views of a dualside-by-side wafer transfer robot and a process module havingside-by-side processing stations at certain wafer transfer operations.

FIG. 6 is a block diagram showing certain components of a control systemused in certain embodiments.

FIG. 7 a is process flow sheet illustrating operations in a method oftransferring wafers from a first location to a second location using twowafer transfer robots.

FIG. 7 b shows a graphical representation of a certain components dualrobot wafer transfer system according to certain embodiments.

DETAILED DESCRIPTION

Overview

Wafer handling systems transfer wafers from the factory floor to processchambers. These systems include loadlocks to bring the wafers fromatmospheric conditions to very low pressure conditions and back, androbots to transfer the wafers to various locations. In transferringwafers from one location to another, wafer transfer robots useprogrammed coordinate information of the loadlocks, process modules,wafer cassettes, or other components to move along a standard path,e.g., from a loadlock to a process module. At certain points, theposition of a wafer may need to be adjusted to correct for wafershifting during robot hand-off, or robot movement with relation to theloadlock, process module or cassette.

Provided herein are methods and apparatuses for wafer positioncorrection that may be used to increase wafer throughput. In certainembodiments, the methods and apparatuses are used in dual wafertransfer, in which two wafers are moved in parallel from one location toanother. For the purposes of discussion, dual wafer transfer isdescribed below, however certain embodiments of the wafer positioncorrection methods and apparatus may be used in single wafer transferand/or transfer of multiple wafers. Given the details and descriptionbelow, one skilled in the art will understand how to implement singleand multiple wafer embodiments.

FIG. 1 shows an exterior of dual wafer handling apparatus and componentsthereof according to aspects of the invention. The apparatus shown inFIG. 1 may be used to transfer wafers from atmospheric conditions (e.g,to and from a storage unit) to one or more processing chambers (e.g.,PECVD chambers) and back again. The apparatus shown in FIG. 1 has threemain components: an atmospheric environment 102, loadlocks 104 and atransfer module 106. Storage units (e.g., Front Opening Unified Pods orFOUPs) and processing chambers are not shown in the figure. Atmosphericenvironment 102 is typically at atmospheric pressure and can interactwith FOUPs and/or parts of the external facility. Transfer module 106 istypically at sub-atmospheric pressure and can be in communication withthe loadlocks and various processing chambers which are often run atvacuum or low pressure. Wafers are placed in loadlocks 104 for pump-downor vent operations when transitioning between atmospheric andsub-atmospheric environments.

The atmospheric environment 102 (also referred to as a‘mini-environment’) contains an atmospheric robot (not shown) thattransfers wafers to and from FOUPs and loadlocks The robot can also beused to transfer wafers to Integrated Metrology Modules, or aligners, orother optional accessories in the mini-environment. Pod loaders 108receive and support FOUPs so that they may be accessed by theatmospheric robot. The atmospheric environment 102 typically contains anoverhead fan filter unit, e.g., a HEPA filter unit, to preventcontaminants from entering the atmospheric environment. The air inlet110 for the fan filter unit is shown in FIG. 1. The lower boundary ofthe atmospheric or mini-environment may be a false floor, such as thatdepicted in FIG. 1 at 112.

Loadlocks 104 receive inbound (unprocessed) wafers from the atmosphericenvironment 102 to be transferred to the process chambers, and outbound(processed) wafers from the transfer module 106 to be transferred backto the FOUPs. A loadlock may be bidirectional (holding inbound andoutbound wafers) or unidirectional (holding only inbound or outboundwafers). In certain embodiments, the loadlocks are unidirectional.Inbound wafers are also referred to herein as incoming or unprocessedwafers; outbound wafers are also referred to herein as outgoing orprocessed wafers.

In FIG. 1, there are two independent loadlocks: an upper loadlockstacked on top of a lower loadlock, each having two connected chambers.In certain embodiments, the upper loadlock is an inbound loadlock andthe lower loadlock is an outbound loadlock. In other embodiments, bothupper and lower loadlocks can be configured as inbound and outbound.Plates 114 are lids of the inbound loadlock, each plate covering one ofthe two connected chambers. Loadlock vacuum pumps 116 are used to pumpdown the loadlocks as necessary during operation.

Atmospheric valve doors 118 provide access to the loadlocks from theatmospheric environment 102. In the embodiment shown, a four door slitvalve externally mounted to the mini-environment is used, though anytype of doors or valves including gate valves, sliding doors, rotationaldoors, etc., may be used.

The transfer module is configured to be attached to one or more processmodules (e.g., single or multi-station PECVD chambers, UV cure chambers,etc.). A process module may be attached to the transfer module 106 atmultiple interface locations/sides of the transfer module. Slit valves122 provide access from the transfer module to the process modules. Anyappropriate valve or door system may be used. In FIG. 1, there are twovalves per side—allowing two wafers to be transferred between a loadlockand a process module (e.g., between two chambers of a loadlock and twoadjacent stations of a process module) or between two process modules.Transfer module lift assembly 120 is used to raise and lower the cover128 of the transfer module. In FIG. 1, cover 128 is down (i.e., theinterior of the transfer module is not shown in the figure). A vacuumtransfer robot is located in the interior of the transfer module totransfer wafers between the loadlocks and the process modules or fromprocess module to process module.

The transfer module 106 is maintained at sub-atmospheric pressure, andis sometimes referred to herein as a vacuum transfer module. Transfermodule pressure is typically between 760 torr-1 miliTorr, though incertain embodiments the tool may be used for even lower pressureregimes. Once an inbound wafer is in place in the loadlock, the loadlockvacuum pumps 116 are used to pump down the loadlock to a sub-atmosphericpressure so that the wafer may be subsequently transferred to the vacuumtransfer module. Loadlock slit valves 122 provide access to theloadlocks from the transfer module 106. Transfer module vacuum pump 124,along with a gas mass flow controller (MFC), a throttle valve and amanometer, are used to obtain and maintain the desired pressure of thetransfer module. In general, on-tool or off-tool vacuum pumps may beused for the transfer module. As is known in the art, various methods ofcontrolling pressure in the transfer module exist. In one example, anMFC provides a constant flow of N₂ gas into the transfer chamber. Themanometer provides feedback as to the pressure of the transfer modulechamber. The vacuum pump removes a constant volume of gas per unit timeas measured in cubic feet per minute. The throttle valve activelymaintains a pressure set point through the use of a closed loop controlsystem. The throttle valve reads the manometer's pressure feedback, andbased on the commands from the valve's control system, adjusts theopening of the effective orifice to the vacuum pump.

An access panel 126 provides access to an electronics bay that containsa control system to control the wafer handling operations, includingrobot movements, pressure, timing, etc. The control system may alsocontrol some or all operations of processes performed in the processmodule. The controllers, switches, and other related electrical hardwarecan be located elsewhere according to various embodiments.

FIGS. 2 a and 2 b are additional schematics of a dual wafer handlingapparatus that show internal views of the atmospheric environment 102and transfer module 106. The apparatus shown in FIGS. 2 a and 2 b isessentially the same as that shown in FIG. 1, with the shape of thetransfer module of the apparatus in FIGS. 2 a and 2 b a trapezoid toallow a larger access 238 area to service the transfer module. Thetransfer module lift assembly and lid, and a portion of the atmosphericenvironment casing are not shown in FIG. 2 a.

The atmospheric environment 102, sometimes referred to as the“Mini-Environment,” contains an atmospheric robot 232. The transfermodule 106 contains a vacuum robot 236. In the embodiment depicted inFIG. 2 a, the atmospheric robot 232 has one arm, with two articulatedwrists, each of which has a paddle or other end effector capable ofcarrying a wafer. Vacuum transfer robot 236 has two arms, each with twopaddles capable of carrying a wafer. The atmospheric robot is capable ofhandling two wafers simultaneously and the vacuum robot cansimultaneously carry up to four wafers. (The apparatus and methodsdescribed herein are not limited to these particular robot designs,though generally each of the robots is capable of handling,transferring, or exchanging at least two wafers.)

FIG. 2 a also provides a partial view of a pipe 244, also referred tothe loadlock pump foreline, that leads from a manifold to the vacuumpumps 244. Dual vacuum pumps 244 work in tandem and are used to pumpdownboth loadlocks According to various embodiments, the the dual pumps mayfunction as a single pump resource or could be dedicated to a specificloadlock for parallel pump downs. FIG. 2 b shows a schematic of theapparatus shown in FIG. 2 a from the opposite side. The transfer modulelift assembly 120 and the transfer module lid 128 are shown in anupright position.

FIGS. 3 a-f are graphical representations showing certain operations indual wafer transport of a pair of wafers from FOUPs to the wafertransfer module and back. FIG. 3 a shows an apparatus with transfermodule 106, upper (inbound) loadlock 104 a, lower (outbound) loadlock104 b and atmospheric environment 102. Also shown are process modules303 a and 303 b. At this point, prior to their entry into atmosphericenvironment 102, wafers are located in e.g., FOUPs 334, which interfacewith the atmospheric environment 102. The atmospheric environment 102contains an atmospheric robot 332; the transfer module 106 contains avacuum robot 336.

As indicated above, the apparatus is capable of parallel transport andprocessing of two wafers. Both the atmospheric and transfer modulevacuum robots are capable of simultaneous handling at least two wafers.

Atmospheric robot 332 has one arm, with two articulated wrists, each ofwhich has gripper capable of carrying a wafer. Vacuum transfer robot 336has two arms, each with two blades or grippers capable of carrying awafer.

The atmospheric robot takes two wafers from FOUPs. (The movement of awafer from a location such as a FOUP, loadlock or processing station toa robot is sometimes referred to herein as a “pick” move, while theplacement of a wafer to a location by the robot is sometimes referred toherein as a “place” move. These moves are also referred to herein as“get” and “put” moves, respectively.) Depending on the robot and thearrangement of the FOUPs or other wafer storage, the two wafers may betaken simultaneously or one after another. In the embodiment depicted inFIG. 3 a, for example, the atmospheric robot has one arm with twoarticulated wrists and is capable of simultaneous transfer of twostacked wafers, e.g., simultaneous picks of two stacked wafers from aFOUP. FIG. 3 b shows the atmospheric robot 332 with two wafers 335′ and335″ during transfer from the FOUP the upper loadlock 104 a. Theatmospheric robot then places the wafers into the upper loadlock 104 afor depressurization. This is shown in FIG. 3 c. One wafer is in eachchamber. Once the wafers are placed in the upper loadlock, theatmospheric doors 118 a of the upper loadlock close and the loadlock ispumped down. When the desired pressure is reached, the upper loadlockdoors 120 a on the transfer module side are open and transfer modulerobot 106 picks the wafers from the upper loadlock. FIG. 3 d showstransfer module robot 106 with wafers 335′ and 335″. The transfer modulerobot depicted in FIGS. 3 a-e has two arms, each with two end effectorsand is capable of holding four wafers simultaneously. In the embodimentshown, the upper loadlock does not have passive wafer centering, nor arethere independent z-drives in the loadlock for each of the wafers.Accordingly, in the embodiment shown, the vaccum robot picks the wafersimultaneously and cannot selectively pick one wafer if two wafers arepresent in the incoming loadlock. However, depending on the robot andthe system, the transfer module robot may pick each wafer simultaneouslyor consecutively. Also depending on the robot and the system, the robotmay use one arm with two end effectors to pick both wafers, or eachwafer may be picked by a different arm. After picking the unprocessedwafers from the inbound loadlock, the transfer module robot transfersthe wafers to a processing module, i.e., either process module 303 a orprocess module 303 b, by rotating and placing the wafers in the processmodule. Although not depicted in FIGS. 3 a-e, there may also be a thirdprocessing module connected to the transfer module. The wafers thenundergo processing in the processing module. FIG. 3 f shows an exampleof a sequence of movements the wafers may undergo in a process module330 a. First, wafer 335′ is placed in station 338 of processing module330 a and wafer 335″ is placed in station 340 of processing module 330a. The wafers then undergo processing at these stations. Wafer 335″moves from station 340 to station 344 and wafer 335′ from station 338 tostation 342′ for further processing. The wafers are then returned totheir original stations to be picked by the transfer module robot fortransfer to the outbound loadlock or to another processing module forfurther processing. For clarity, the stations are depicted as ‘empty’ inthe figure when not occupied by wafers 335′ and 335″, in operation allstations are typically filled by wafers. The sequence illustrated inFIG. 4 is just an example of a possible sequence that may be employedwith the apparatuses described herein. The transfer module robot picksboth wafers up for simultaneous transfer to the loadlock. The pick movesmay occur simultaneously or consecutively. The robot then rotates toplace the processed wafers in the loadlock. Again, these moves may occursimultaneously or consecutively according to various embodiments. FIG. 3e shows the now processed wafers 335′ and 335″ placed in the outbound(lower) loadlock 104 b. After being placed there, all loadlock valves ordoors are shut and the outbound loadlock is vented (pressurized) toatmospheric pressure. The wafers may also be cooled here. Theatmospheric doors of the outbound loadlock are then opened, and theatmospheric robot picks up the processed wafers and transfers them tothe appropriate place in the FOUP.

Wafer position correction may occur at various points in the processdescribed above. According to embodiments described further below,inbound wafer position is corrected at placement into the process moduleby the transfer module robot. According to various embodiments describedfurther below, outbound wafer position is corrected during the pick movefrom the loadlock by the ATM robot. Wafer position may also be correctedat other points during transfer instead of or in addition to thesepoints.

In certain embodiments, the loadlocks are used in unidirectionaloperation mode. An example of inbound and outbound loadlocks,atmospheric robot and transfer module robot moves in a unidirectionalflow scheme is given below in Table 1:

TABLE 1 Robot and Loadlocks Moves in Unidirectional Flow Operation ATMRobot Incoming LL (Upper) Outgoing LL (Lower) TM Robot FOUP Pick (1)Vent (Empty) TM Robot Lower LL Place (arm 2) Upper LL Place (2) ATMRobot (2) Vent/Cool (Wafers) PM Pick (arm 2) Lower LL Pick Pumpdown(Wafers) (3) ATM Robot PM Place (arm 1) FOUP Place TM Robot (4) Pumpdown(Empty) Upper LL Pick (arm 1) (4) FOUP Pick Vent (Empty) TM Robot LowerLL Place (arm 2) Upper LL Place ATM Robot Vent/Cool (Wafers) PM Pick(arm 2) (1′) Lower LL Pick Pumpdown (Wafers) ATM Robot PM Place (arm 1)(5) FOUP Place TM Robot Pumpdown (Empty) Upper LL Pick (arm 1) FOUP PickVent (Empty) TM Robot Lower LL Place (arm 2) (2′) Upper LL Place ATMRobot Vent/Cool (Wafers) (3′) PM Pick (arm 2) Lower LL Pick (4′)Pumpdown (Wafers) ATM Robot (4′) PM Place (arm 1) FOUP Place (5′) TMRobot Pumpdown (Empty) Upper LL Pick (arm 1)

Table 1 presents an example of a sequence of unidirectional operationalmode in which the transfer module robot hand-off sequence is processmodule (wafer exchange)→outgoing loadlock (place processedwafers)→incoming loadlock (pick unprocessed wafers). This is an exampleof one possible sequence—others may be used with the dual wafer handlingapparatuses described herein, including outgoing loadlock accessedbefore the incoming loadlock.

Rows can be read as roughly simultaneously occurring or overlappingoperations. Columns show the sequence of operations the robot orloadlock performs. Of course, in any system, these operations may notoverlap exactly and one or more of the modules may be idle or begin orend later. Further, it should be noted that certain operations are notshown. The rotational and translational moves the robots must perform toreach the pods, loadlocks and process modules are not shown. Thedescriptions ‘TM Robot’ and ‘ATM Robot’ can refer to the moves theloadlocks undergo—opening and closing the appropriate doors—as well asadmitting the robot end effectors to pick or place the wafers.

The path of a pair of unprocessed wafers going from a FOUP to a processmodule is traced in the Table in steps 1-5:

1—ATM Robot FOUP Pick

2—ATM Robot Upper Loadlock Place

3—Upper LL Pumpdown (see FIG. 3 c)

4—TM Robot Pick

5—TM Robot Process Module Place

The path of a pair of processed wafers going from a process module to aFOUP is traced in the Table in steps 140 -5′:

1′—TM Robot Process Module Pick

2′—TM Robot Lower LL Place

3′—Lower LL Vent/Cool (see FIG. 3 e)

4′—ATM Robot Lower LL Pick

5′—ATM Robot FOUP Place

As can be seen from the Table 1, once outgoing wafers are handed off toan atmospheric robot, for example, the loadlock can then be pumpeddown—it does not have to wait for the atmospheric robot to complete itsmoves before pumping down. This is distinguished from some types ofbidirectional operation in which a loadlock is idle while theatmospheric robot places the processed wafers in a FOUP or othercassette and gets two unprocessed wafers from a cassette for placementinto the loadlock. Various robot and loadlock moves according to certainembodiments are described below.

Incoming LL

Pumpdown: Pressure in the upper loadlock is lowered from atmospheric toa predetermined subatmospheric pressure. This pumpdown operation israpid.

Vent: Vent the upper loadlock from a subatmospheric pressure toatmospheric. No wafer is present. The upper loadlock may be ventedradially as described below with reference to FIG. 6 a. Like the pumpdown operation, the vent operation is fairly rapid.

Outgoing LL

Vent/Cool: Vent the lower loadlock from a subatmospheric pressure toatmospheric pressure. Venting is done by flowing gases such as heliumand/or nitrogen into the chamber. The wafers enter the lower loadlockneeding to be cooled from processing.

In one embodiment, helium is first vented into the chamber as a heattransfer gas, to an intermediate pressure. Gas flow is then stoppedwhile the wafer cools. Nitrogen is then flowed to get the pressure up toatmospheric.

Pumpdown: Pump the lower loadlock from atmospheric to a pre-determinedsubatmospheric pressure. The chambers are empty.

ATM Robot

FOUP Pick: The atmospheric robot picks two stacked unprocessed wafersfrom a FOUP or other cassette. In one embodiment, the end effectors arestacked on top of the other and pick the stacked wafers simultaneously.After picking the wafers, the end effectors are rotated with respect toeach other, and the arm is rotated to place the wafers in the upperloadlock (see FIG. 3 b, which shows a single arm dual end effector robotholding two wafers ready to place them into the upper loadlock). Incertain embodiments, the wafers are picked consecutively in either order(e.g., where the ATM robot is a stacked dual end effector robot).

Upper LL Place: The atmospheric robot places the wafers into the upperloadlock chambers. In certain embodiments, first one end effector isextended into a chamber of the upper loadlock and lowers the wafer ontothe shelf. The end effector is then retracted from the loadlock and thesecond end effector is extended into the other chamber of the upperloadlock and lowers the wafer onto the shelf.

Lower LL Pick: The atmospheric robot picks the wafers from the lowerloadlock chambers. First one end effector is extended into a chamber ofthe upper loadlock and picks the wafer from the pedestal, which incertain embodiments may involve picking the wafer from a wafer liftmechanism that has lifted the wafer from the pedestal. The end effectoris then retracted from the loadlock and the second end effector isextended into the other chamber of the lower loadlock and picks thewafer from the pedestal or lift mechanism. In certain embodiments, therobot uses information about the placement of each wafer in the lowerloadlock to correct wafer position during the pick move. The atmosphericrobot arm is then rotated to place the wafers in the FOUP.

FOUP Place: The atmospheric robot places the wafers into stackedpositions in a FOUP. In one embodiment, both wafers are placedsimultaneously.

Transfer Module Robot

Upper LL Pick: The transfer module robot extends one dual end effectorarm into the upper loadlock and lifts the wafers from the shelves ontothe end effectors. In certain embodiments, as one arm is extended intothe loadlock, the other arm moves into a retracted position. FIG. 3 gshows a dual arm dual end effector robot with one arm extended (e.g.,into a loadlock or process module for a pick or place move) and one armretracted. In the scheme shown in Table 1, one arm is dedicated totaking unprocessed wafers from the upper loadlock and placing them inthe process module (arm 1), and the other dedicated to taking processedwafers from the process module and placing them in the lower loadlock(arm 2). In other embodiments, both arms may be used for processed andunprocessed wafers. In the scheme shown in Table 1, after the upperloadlock pick move, the arm 1 retracts and arm 2 is extended into thelower loadlock to place processed wafers there.

Lower LL Place: The transfer module robot extends arm 2—having aprocessed wafer on each end effector—into the lower loadlock and placesthem there. In certain embodiments, this is done simultaneously.Position information of each wafer loadlock may be measured and storedfor use by the atmospheric robot in picking the wafers. The robot isthen positioned for the process module pick move. In certain schemes,the wafers' positions may be independently corrected prior to placementby using the wafer lifts independently.

Process Module Pick: The transfer module robot extends arm 2 into theprocess module and picks the two processed wafers. In certainembodiments, this is done simultaneously. In the scheme shown in Table1, after the process module pick, the transfer module robot places theunprocessed wafers into the process module.

Process Module Place: The transfer module robot extends arm 1—having twounprocessed wafers—into the process module and places them at thestations (as in FIG. 4) either by lower the wafers onto the stations, orby wafer supports in the stations lifting the wafers off the endeffectors. In certain embodiments, the place moves are done sequentiallyto allow position corrections to be made in each place move.

FIGS. 1-3 and the associated discussion provide a broad overview of thedual wafer processing apparatus and methods discussed herein. Details ofthe transfer methods according to various embodiments have been omittedand are discussed in further detail below, including wafer pick andplace moves, wafer alignment, pressurization and depressurizationcycles, etc. Additional details of the apparatus according to variousembodiments are also discussed below.

FIGS. 4 a and 4 b show an example of a loadlock assembly having stackedindependent loadlocks. In FIGS. 4 a and 4 b, the transfer module side ofthe loadlock assembly faces front. As described above, each loadlock hastwo connected chambers. Lids 114 each cover one chamber of the upperloadlock. Slit valves 120 show valves allowing access from the loadlockto the transfer module on the left side of the loadlocks. The valves onthe right side are not shown in the figure to provide a view of thehousing 450 and the loadlock assembly openings 452 in the housing 450.In certain embodiments, the slit valves may be independently controlledbut tied together pneumatically. Isolation manifold 454 leads to theloadlock pump is used for equilibration and pumpdown operations. Sideports 456 allow viewing of the interior of the loadlock. Lower loadlocklift mechanism 458 is used to raise and lower the wafers from the coolplate to allow robot end effectors the clearance to pick and placewafers. This allows for a cool plate without large clearances cut forthe end effectors. As described further below, in certain embodiments,the loadlock chambers are tolerant of a range of wafer positions, e.g.,a transfer module robot may place the wafers in the loadlock without anyposition correction. The loadlock may be configured to tolerate theoffset wafer position without any centering. Position correction maythen be made during the pick from the loadlock by the atmospheric robot.

Wafer Position Correction

FIGS. 3 a-3 f and accompanying description above describe various waferhandling tasks, including pick and place moves. In performing thevarious wafer handling tasks described herein, the wafer transfer robotsuse programmed coordinate information of the loadlocks, process modules,FOUPs, etc. Using this information and its present position, a robot canmove along a nominal or standard path to move a wafer from one locationto another. At certain points, the position of a wafer may need to beadjusted to correct for wafer shifting during robot hand-off, robotmovement or in a loadlock, process module or cassette. Wafer positioncorrection may be accomplished in a variety of manners—for example, U.S.Pat. No. 6,405,101, hereby incorporated by reference, describes a wafercentering system in which sensors are used to detect the edges of thewafer as the wafer is passed over the sensors. This edge detectioninformation is then used to modify the place move to compensate for anydeviation of the wafer from a reference position. Some systems usemechanical centering methods—for example, self-centering methods inwhich a wafer is guided into position after hand-off by a sloped surfaceor pads at the loadlock, process module or other destination station.Other systems rely on a dual-edge gripper in which a wafer is picked upand then gripped—thereby forcing the wafer into a set position.

According to various embodiments, methods of correcting wafer positionat certain points using a dual wafer transport apparatus are described.In certain embodiments, the methods involve correcting positions atplacement at a location (e.g., in a process module). In certainembodiments, the methods are used with loadlocks that tolerateoff-center wafers, and make corrections at placement into the processmodule and wafer cassette stations.

In certain embodiments, methods of performing place moves using dualside-by-side end effector robots with active wafer position correctionare described. These methods may be used for placement into a processmodule, loadlock or other destination by a dual wafer transfer modulerobot. As indicated above, in certain embodiments, the loadlocks(incoming or outgoing loadlock) is tolerant of off-center wafers andplacement of the wafers into the outgoing loadlock is performed withoutcorrection.

As described above, in certain embodiments, the transfer module robothas dual side-by-side end effectors on each arm. The robot can providenearly double the throughput of a single wafer transfer robot bytransferring two wafers with the same number of moves. The end effectorsare fixed relative to each other and therefore move in unison. A dualend effector robot holding two wafers, one on each end effector, extendsthe end effectors along a nominal path. The nominal path is apreprogrammed standard path for moving from a first location, e.g., aloadlock, to a second location, e.g., a process module. The nominal pathtypically includes a rotational motion and then a radial or extensionmotion into the placement position. The hand-off is then accomplished bythe robot lowering the wafers onto wafer supports or by lift pins at thedestination stations lifting each wafer off its end effector.

FIG. 5 a is a flowchart showing operations in a method of active wafercenter position correction wafer position using a dual side-by-side endeffector robot. The method begins at block 502 in which the wafers onthe dual end effectors are extended along the nominal path into theprocess module or other location. The robot has input and output linesfor reading sensors and sending position information to a processor. Asthe robot is extended along the nominal path, sensors measure theposition of both wafers. The information is collected. This is indicatedat blocks 504 and 506. In the process shown in FIG. 5 a, the datacollection of wafer 2's position is offset from that of wafer 1, e.g.,by 10 mm. This is to avoid overwhelming the sensing and data collectionhardware and software. However, in certain embodiments, the positionsmay be measured simultaneously. Also, position measurement is notlimited to the extension move—for example, wafer positions can bemeasured during the retraction path from the loadlock during the pickmove, or at another point along the nominal path.

The position information may include wafer edge detection information.See, e.g., above-referenced U.S. Pat. No. 6,405,101. After the waferpositions are sensed, the processor receives this information and thencalculates the placement correction necessary for both wafers. Block508. Small rotational and extension (radial) corrections are made asnecessary to center wafer 1 correctly over the pedestal or other wafersupport. Block 510. Wafer 1 is then placed at its station, while wafer 2remains on its paddle or other end effector. Block 512. In certainembodiments, placing the wafer at its station involves the station liftpins lifting the wafer from the end effector. Small rotational andextension (radial) corrections are then made as necessary to centerwafer 2 at its station. Wafer 2 is then placed at its station. Block516. The robot arm is retracted with the wafers staying at thedestination. Block 518. Placement of the wafers may be accomplished bylowering each wafer to a fixed support, or by using independentlycontrolled lift devices. If the former is used, the fixed supports areat different heights such that wafer 2 remains on the end effector whenthe end effectors are lowered to place wafer 1. If independentlycontrolled lift pins are used, the lift pins or other lift device raisesto lift the applicable wafer off its end effectors. The lift devices maylower the wafers after the end effectors have been retracted.

FIG. 5 b shows illustrations of certain operations discussed inreference to FIG. 5 a. FIG. 5 b shows the dual end effectors on therobot arm 562 holding wafers 1 and 2. At 550, the robot arm is in aretract position. Hand-off locations (e.g., process module stations) areindicated at 568 and 570. The dotted circles indicate an unoccupiedwafer location. Next, at 552, the robot arm 562 is extended into theprocess module and has been extended or rotated as necessary to placewafer I (in grey) in the correct hand-off position. At 554, lift pins(not shown) have lifted wafer 1 from its end effector and the robot hasbeen further extended and rotated to place wafer 2 is in its correcthand-off position. At 556, the robot arm 562 is retracted. The wafersstay at their respective stations.

In certain embodiments, the robot communicates with the lift pins ateach destination wafer station to lift and lower the pins. FIG. 6 showsa block diagram illustrating control of the lift pins according tocertain embodiments. Platform controller (PC) 602 is the main controllerfor the entire tool including the wafer handling apparatus and theprocess modules to which it is coupled. Platform controller 602 acts asthe system controller, which controls scheduling, tells the processmodule controllers what process to perform on a wafer, etc., as well asa module controller for the wafer handling apparatus.

Platform controller 602 sends commands to process module controllers(ECs) 610, 612 and 614 and the transfer module robot 606 via switch 604.(Other parts of the tool that the process controller may control are notshown in this figure). Each EC controls a process module: EC 610controls process module 1 (PM1), EC 612 controls PM2 and EC 614 controlsPM3. There are typically multiple input/output controllers (IOCs) ineach module as indicated in FIG. 6 for connecting to the individualvalves, sensors, etc. in each module. The controllers can be physicallylocated at various points in the apparatus; e.g., within the processmodule or on a stand-alone rack standing at some distance away from themodule.

The lift pins for each process module are indicated at 616 (PM1), 618(PM2) and 620 (PM3). Each process module typically has a set of liftpins for each station within the module. Each set may be independentlycontrolled. TM Robot 606 can control the lift pins as indicated by thebold connection lines in the figure. The lift pins thus have twomasters—the process module and the transfer module robot. In certainembodiments, a dual end effector transfer module robot controls the liftpins during place moves to perform staggered independent wafercorrections as described above.

The above described methods may be used when placing wafers at alocation (e.g., a process or other module) using a dual side-by-side endeffector robot, such as that shown in FIG. 5 b. Wafer position error ismeasured prior to the place, and then the place moves are performedindependently.

Another method of correcting wafer position error involves measuringwafer position error on a robot, e.g. a dual side-by-side end effectorrobot, during transfer to an intermediate station. This measurement datais then used by a second robot to perform wafer pick moves from theintermediate station with corrections to center the wafer. FIG. 7 a is aflowchart showing operations in a method of wafer position correctionusing two robots and an intermediate transfer station. First, a robot(Robot A) having dual end effectors each holding a wafer extends the endeffectors into nominal hand-off positions at the intermediate location.Block 702. In certain embodiments, the Robot A has dual side-by-side endeffectors fixed relative to one another, though the methods describedare not limited to such a robot. During the extension process, thelocation of each wafer on the effector is measured. Block 704. In otherembodiments, the location data may be read at other points—for example,during a retraction from a previous location (e.g., a process module) orduring transfer from a previous location to the intermediate location.After the end effectors have been extended to the nominal hand-offposition, the wafers are placed at the intermediate location. Block 708.Note that the wafer positions are as yet uncorrected—thus, theintermediate location should be tolerant of offset wafers. Returning tothe right side of the flowchart, after the location data is measured,location error data is fed to Robot B. The error data may include thepositions of the wafers on the end effectors and/or calculatedcorrections (based on position information) to the pick moves Robot Bwill make. Using the error data and/or calculated corrections, Robot Bpicks the wafers from the intermediate location with offsets to correctlocation error. Block 710. Unlike the place moves to the intermediatelocation (block 708), which may be simultaneous, the wafers are pickedconsecutively so that the necessary rotational and extension adjustmentsto pick up each wafer may be performed. (If Robot B is capable ofperforming these adjustments and pick moves simultaneously, the pickmoves may be simultaneous.) Because Robot B received location errorinformation from Robot A, and picked the wafers to adjust for the error,the wafer positions on the end effectors are correct. Robot B thentransfers the wafers to a location C, and places them there. Block 712.Because the wafer positions on the end effectors of Robot B are correct,the wafers are placed without the need for additional corrections andmay be placed simultaneously. In many embodiments, the adjustments madeby Robot A are made based solely on the measurements made in operation704; however in certain embodiments the adjustments made by Robot B mayalso take into account other measurements or standard adjustmentfactors, e.g., to account for any shifting that takes place within theintermediate location.

FIG. 7 b illustrates a dual robot system in which the above-describedmethod may be used. Here, Robot A is a dual side-by-side end effectorrobot, wherein the end effectors are fixed relative to each other. It iscapable of simultaneous pick and place moves of two wafers inside-by-side locations. In certain embodiments, this robot is a transfermodule robot used to transfer wafers between a loadlock and one or moreprocess modules. In certain embodiments, the robot has more than onearm, each arm having dual end effectors such as described above in FIG.3 g. The intermediate station in FIG. 7 b is a loadlock havingside-by-side chambers to hold each of the wafers. One such loadlock isdepicted above in FIGS. 4 a and b. Robot B in the example of FIG. 7 b isa stacked dual end effector robot. In certain embodiments, this robot isan atmospheric robot that transfers wafers between the loadlock and astacked wafer location, e.g., a FOUP or cassette. The wafer flow schemesdescribed above in reference to FIGS. 3 a-3 f may be used with thisarrangement. The system shown in FIG. 7 b is one example of possiblearrangements of dual robots in which a first robot places one or morewafers in an intermediate location with position error measurement butnot correction, and a second robot picks the one or more wafers withcorrection based on that measurement. With dual end effector robots,each of the robots may have side-to-side end effectors or stacked endeffectors.

The methods and systems described above allow wafer corrections to bemade at only one location—if Robot A is a wafer throughput limiter, thissystem improves the throughput by avoiding performing the corrections atthe Robot A hand-off to intermediate station B. Further, correctingwafer position at the intermediate station would require some mechanismwithin the place location (e.g., a pin lift) to allow for consecutivesingle wafer transfers (e.g., extend arm to intermediate station withcorrection. The methods described above also allow Robot B to perform asimultaneous place move to location D with the wafers accuratelypositioned. These advantages are not limited to the system describedabove, but apply to other systems in which Robot A is a throughputlimiter and/or position correction mechanisms at the intermediatestation are undesired.

As indicated above, the intermediate station should be tolerant of arange of wafer positions. In certain embodiments, this means that thewafer rests substantially where placed by the Robot A—without sliding orself-centering on a sloped surface or pads. The shape and position ofthe load lock walls are such that a grossly misplaced wafer (e.g., >6mm) will still clear. For example, if it is possible for the transfermodule robot to have one wafer placed 6 mm one direction, and the otherwafer 6 mm the other direction, the load lock has 12 mm of clearance inall directions. If wafer position is corrected sequentially in thisscenario, the wafer being corrected second must have a full 12 mm ofclearance. The wafer cooling plates and handoff pins are also designedto be tolerant of misplaced wafers. Wafer gap to the cooling plate iscritical to proper wafer cooling. The rest pins for the wafer aredesigned with a down slope, e.g., of one degree. The down slope isenough of an angle to prevent backside contact of a highly dished waferand is shallow enough so that if a wafer is misplaced by up to 6 mm, thechange in gap along that slope is negligible.

In certain embodiments, a controller is employed to control aspects ofthe wafer transfer and position error correction processes describedabove. The controller will typically include one or more memory devicesand one or more processors. The processor may include a CPU or computer,analog and/or digital input/output connections, stepper motor controllerboards, etc. The controller executes system control software includingsets of instructions for controlling the timing, Other computer programsstored on memory devices associated with the controller may be employedin some embodiments. In certain embodiments, there will be a userinterface associated with the controller. The user interface may includea display screen, graphical software displays of the apparatus and/orprocess conditions, and user input devices such as pointing devices,keyboards, touch screens, microphones, etc.

The computer program code for controlling the transfer and positionerror correction and other processes in a process sequence can bewritten in any conventional computer readable programming language: forexample, assembly language, C, C++, Pascal, Fortran or others. Compiledobject code or script is executed by the processor to perform the tasksidentified in the program. Parameters may be provided to the user in theform of a recipe, and may be entered utilizing the user interface.Examples of parameters that may be provided to or entered by the userinclude the time delay for wafer cooling, time delay between a switchclosing and a valve opening, the trigger point for a pressure controlsystem to close a valve, a pressure setpoint for a throttle valve, and aflow setpoint for a mass flow controller. Signals for monitoring theprocess may be provided by analog and/or digital input connections ofthe system controller. The signals for controlling the process areoutput on the analog and digital output connections of the apparatus.The system software may be designed or configured in many differentways. For example, various transfer apparatus component subroutines orcontrol objects may be written to control operation of the apparatuscomponents necessary to carry out the inventive transfer processes.Examples of programs or sections of programs for this purpose includerobot positioning code, wafer positioning code, wafer position detectioncode, position information transfer code. A system controller may alsoinclude code to run pumpdown/vent or process module operations. A robotpositioning program may include program code for moving the robot alonga path, e.g., a nominal (standard) path or along a path as dictated byposition correction calculations. A wafer positioning program mayinclude program code for controlling robot and chamber components, suchas lift pins, that are used to place or pick the wafer to or from apedestal, chuck or support and to control the spacing between thesubstrate. A wafer position detection program may include code formeasuring the position of a wafer on an end effector. A wafer correctionprogram may include code for determining rotation andextension/retraction adjustments a robot should make based on measuredposition information. A position information transfer program mayinclude code for storing, sending and/or receiving position detectioninformation to a second robot.

In certain embodiments, a series of programs may be associated with anyor each of the following modules: the mini-environment, inbound loadlock, outbout load lock, transfer module and each process module, with aeach of these capable of running a single program at a time. Forexample, an inbound load lock may have a vent program and a pumpdownprogram.

A higher level scheduler program may include code for receiving orobtaining information about wafers and process recipes and code forinstructing certain modules to run the appropriate programs. Forexample, code may include instructions for the transfer module robotexchange wafers program can exchange wafers with a process module, whilethe atmospheric robot is picking wafers from a FOUP. Scheduler rules andlogic generally prevent two robots from trying to access the same loadlock at the same time, unless the action is intentional. The schedulerprogram code includes checks to ensure process operations occur in theproper sequence, e.g., that a vent on a load lock is executed beforeexecuting an ATM place wafer program to that load lock.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. It should be noted that there are many alternative waysof implementing both the process and apparatus of the present invention.Accordingly, the present embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalents of the appended claims.

1. A method of transferring wafers from a first location to a secondlocation, comprising: a) extending a dual end effector arm of a firstrobot to a first location having first and second side-by-side wafers topick the wafers such that each wafer is supported by an end effector; b)retracting the dual end effector arm along a nominal path and moving thedual end effector arm along a nominal path to an intermediate station;c) extending the dual end effector arm along a nominal path tosimultaneously place the wafers at the intermediate location; whereinposition information of the wafers relative to the end effectors ismeasured at some point during the nominal retraction, transfer orextension moves; d) sending the position information to a second robotand receiving the position information with the second robot; e) pickingthe first wafer from the intermediate location with a first end effectorof the second robot to from the intermediate location, wherein theposition of the end effector during the pick move is adjusted based onthe received position information; f) picking the second wafer from theintermediate location with a first end effector of the second robot tofrom the intermediate location, wherein the position of the end effectorduring the pick move is adjusted based on the received positioninformation; f) transferring the wafers to the second location along anominal path; and h) simultaneously placing the wafers at the secondlocation.
 2. The method of claim 1 wherein the dual end effectors of thedual end effector arm of the first robot are fixed with respect to eachother.
 3. The method of claim 1 wherein the second robot is capable ofsingle wafer transfers and simultaneous transfers of two stacked wafers.4. The method of claim 1 wherein the first and second end effectors ofthe second robot are stacked end effectors.
 5. The method of claim 1wherein the first and second end effectors of the second robot areindependently articulated end effectors on a single arm.
 6. The methodof claim 1 wherein the second robot comprises multiple stacked singleend effector arms.
 7. The method of claim 1 wherein the intermediatelocation is a loadlock.
 8. The method of claim 1 wherein the secondlocation has stacked supports for holding wafers in a stackedconfiguration.
 9. The method of claim 1 wherein the second location is aFOUP or wafer cassette.
 10. The method of claim 1 wherein theintermediate location does not have wafer lift mechanisms.
 11. Anapparatus for transferring two wafers from a first location to a secondlocation, comprising: a) first location having side-by-side waferstations; b) a dual side-by-side end effector robot, wherein said dualend effectors positions are fixed relative to each other; c) anintermediate station having side-by-side wafer stations; d) a secondrobot; and c) a controller for controlling the transfer of the wafers,wherein said controller controls extending a dual end effector arm of afirst robot to the first location having two side-by-side wafers to pickthe wafers such that each wafer is supported by an end effector;retracting the dual end effector arm along a nominal path and moving thedual end effector arm along a nominal path to an intermediate station;extending the dual end effector arm along a nominal path to place thewafers at the intermediate location; wherein position information of thewafers relative to the end effectors is measured at some point duringthe nominal retraction, transfer or extension moves; storing theposition information; picking a first wafer from the intermediatelocation with a first end effector of the second robot to from theintermediate location, wherein the position of the end effector duringthe pick move is adjusted based on the position information; picking asecond wafer from the intermediate location with a first end effector ofthe second robot to from the intermediate location, wherein the positionof the end effector during the pick move is adjusted based on the storedposition information; transferring the wafers to the second locationalong a nominal path; and simultaneously placing the wafers at thesecond location.
 12. A method of transferring wafers from a firstlocation to a second location, comprising: a) extending an arm of afirst robot to a first location having one or more wafers to pick theone or more wafers such that each wafer is supported by an end effector;b) retracting the arm along a nominal path and moving the arm along anominal path to an intermediate station; c) extending the arm along anominal path to place the one or more wafers at the intermediatelocation; wherein position information of the one or more wafersrelative to its respective end effector is measured at some point duringthe nominal retraction, transfer or extension moves; d) storing and/orsending the position information to a second robot; e) picking the oneor more wafers from the intermediate location with a second robotwherein picking the one or more wafers comprises adjusting an endeffector based on the position information of the wafer being pickedsuch that each wafer is centered on the end effector; f) transferringthe one or more wafers to the second location along a nominal path; andg) placing the one or more wafers at the second location.
 13. The methodof claim 12 wherein the arm of the first robot has dual side-by-side endeffectors that are fixed relative to one another.
 14. The method ofclaim 13 wherein the first location is a loadlock having side-by-sidewafer stations.
 15. The method of claim 13 wherein (a) comprisessimultaneously picking two side-by-side wafers from the first location.16. The method of claim 13 wherein the second robot has two stacked endeffectors.
 17. The method of claim 13 wherein (e) comprises picking twowafers consecutively.
 18. The method of claim 13 wherein (g) comprisessimultaneously placing two wafers at the second location.
 19. A methodof transferring wafers from a first location to a second location,comprising: measuring wafer position information of one or more wafershandled by a first robot during transfer from the first location to anintermediate location and picking the one or more wafers from theintermediate location with a second robot for transfer to the secondlocation, wherein picking the one or more wafers comprises using themeasured position information to determine the trajectory of one or moreend effectors of the second robot during the pick move.